Towing Techniques - Wikispaces · Towing Techniques – Version 1 (2013) ... 10.4 Vessel at Anchor...

Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014

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Towing Techniques

Contents Overview .................................................................................... 2

1. Coastguard Policy ................................................................... 2

2. Towing Configurations ........................................................... 2

2.1 Straight Tow ........................................................................ 2

2.2 Fixed Bridle or ‘Y’ Tow ........................................................ 2

2.3 Adjustable Bridle ................................................................. 3

3. Line Handling .......................................................................... 3

3.1 Hazards ............................................................................... 3

3.2 Chafe Gear .......................................................................... 4

4 Messenger Lines ...................................................................... 4

5. Catenary Devices .................................................................... 5

6. Drogues .................................................................................. 5

7. Kicker Hook ............................................................................ 5

8. Towing Equipment Maintenance .......................................... 6

9 Forces in Towing ..................................................................... 7

9.1 Yawing ................................................................................. 7

9.2 Burying the Bow .................................................................. 7

9.3 Stopping and Swamping ..................................................... 8

9.4 Being Overtaken by the Tow .............................................. 8

9.5 Towing Speed ...................................................................... 9

10. Towing Situations ................................................................ 9

10.1 Sinking Tow ....................................................................... 9

10.2 Vessel Aground ................................................................. 9

10.3 Heeling a Vessel Aground ............................................... 10

10.4 Vessel at Anchor ............................................................. 11

10.5 Towing Alongside or Barging .......................................... 11

10.6 Berthing a Tow ................................................................ 12

11. Summary of Standard Towing Practice ............................. 12

Towing is

potentially

hazardous to both

vessels and all

crew involved,

therefore

knowledge of safe

towing procedures

is paramount for

all CRV crew.

Constructive

feedback and

suggestions for

improvements to

the SAR Training

Matrix is

appreciated. Please

email feedback /

suggestions to

sartrainingfeedback

@coastguard.co.nz

providing as much

detail as possible.

Thank you.

mailto:[email protected]

mailto:[email protected]


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Overview

Towing is potentially hazardous to both vessels and all crew involved, therefore knowledge of safe towing procedures is paramount for all CRV crew.

1. Coastguard Policy

The primary responsibility of Coastguard during a SAR operation is the

preservation of life. The Skipper of the CRV must consider the possible

danger to people on board the disabled vessel and decide whether to

tow the disabled vessel and its crew, or to transfer those people to the

CRV.

A tow operation to remove a vessel and crew from danger is only strictly

a SAR operation until reaching the nearest safe haven. To continue the

tow beyond this point must be within the Unit SOP, regional policy, and

agreed by the skippers of both vessels.

2. Towing Configurations

The most common arrangements for towing fixtures on the CRV are:

2.1 Straight Tow The towline is made fast to a single fitting (bollard), often positioned on

the centreline some way forward of the vessel’s transom. This

arrangement allows the stern to swing while towing. This will give

greater control and manoeuvrability than if the towline is attached

directly to the stern.

2.2 Fixed Bridle or ‘Y’ Tow The bridle is made fast to the CRV quarter cleats. The towline is attached

to the apex of the bridle. The main towline is a set length and any

adjustments to the towline length are made using the bridle line. A

disadvantage of this method is that to lengthen the towline by 5m you

may end up paying out almost 10m of bridle line. The advantage is that

Maritime

Regulations

Maritime Rule 22

’Collision

Prevention’ provides

the steering and

sailing rules for

towing, while the

standards for

installation,

performance and

use of lights and

sound signals are

covered by Rule

22.24 ‘Towing and

Pushing’.

“One safety rule

that must be

followed when

making up the

bridles is that the

length of each leg

of the bridle must

be at least one and

one half times the

width of the tow.

For a barge with a

beam of 50 feet,

each bridle leg

would be at least

75 feet long.”

FM55-501Marine

Crewman’s

Handbook (1999)

Dept. of the Army,

Washington.


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the strain of the tow will be equally divided between the two quarter

cleats.

2.3 Adjustable Bridle An adjustable bridle which allows the towline length to vary is more

desirable but has the complexity of dealing with blocks and extra line.

The bridle can be made up of a block permanently attached on the end

of the main towline with the bridle line being lead through the block.

Another method for an adjustable bridle is to pass the main towline

lead through the block where it is tied off to one of the quarter cleats.

The other line from the block is tied to the other quarter cleat – this

block line can be adjusted to ensure the tow line is centred.

By using this method the amount of line needed on board the CRV for

towline adjustment is reduced, but the strain imposed by the tow will

not be equally divided between the two quarter cleats because the

majority of the strain will be on the cleat taking the main towline.

3. Line Handling

3.1 Hazards Whatever method is used for towing, care must be

exercised when attaching the towline to the CRV so that

the towline’s lead is ‘fair’. This will reduce the chance of

the towline trapping itself on the cleat or post.

All CRV crew should be aware of the potential hazard of the towline

parting and its subsequent recoil. Great care must be taken to ensure

the towline is stowed correctly and is free to run at all times.

Avoid putting yourself in a position where a parting line and

subsequent recoil will put you at risk.

Do not handle lines under load close up to the fitting; always

keep a safe distance between the fitting and your fingers.

“The Towline can

be a deadly killer

and many forget

how quickly things

can go wrong when

a line is under load.

The crew must

ensure all gear

(lines, shackles,

messenger,

drogues, tow bits,

chafing gear,

fairleads, etc.) have

been checked for

wear and tear.”

Canadian Coast Guard

Auxiliary Search &

Rescue Crew Manual

Activity:

Towline safety

Towing can be deadly

and it is vital all gear is

checked and crew

operate safe practices.

• Divide a whiteboard

into two columns.

Label one ‘Towing

Gear’ and the other

‘Line Handling’

• Ask the crew to think

about all those safety

aspects that should

be considered as they

prepare for a tow.

• Some examples for

‘Towing gear’ are

towline is attached to

designated strong

point on CRV and

towed vessel, use

your own towline if

possible, towline

should be clean and

free from debris, no

chafing, towing eye

used where possible

rather than knots

• Some examples for

‘Line Handling’

include never use

hitches to secure a

towline, avoid

adjusting length of

tow while underway,

always stay out of the

bight (turn) especially

around tow post,

never handle lines

close to fittings etc.

• Once the lists are

generated discuss

crew responsibilities

and how safety can

be managed.


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If gloves are to be worn, they should only be close fitting finger-

less type gloves which will not become trapped by a line.

3.2 Chafe Gear Any towline in use can be subject to high loading and consequently

suffer damage from chafe on the towed vessel’s fairleads or stem fitting.

One of the most cost effective and robust types of chafe gear is simple

flexible plastic hosing. The hosing can be already on the towline when it

is passed and subsequently held in position with a simple clove hitch or

preferably a rolling hitch (or any form of lashing that keeps it in place).

If hosing or similar is not available, any suitable chafe gear should be

considered such as old towels or clothing. It can take only a few minutes

to seriously damage a line exposed to chafe.

4 Messenger Lines

A messenger line is simply a length of light line attached to the towline

that can be thrown, propelled or floated to a vessel or person.

A heaving line is a light line with a ‘monkey’s fist’, sand pouch, or similar

weight at the throwing end. The other end of the heaving line is secured

to the towline. Securing the heaving line approximately one metre from

the towline eye will enable the eye to be placed directly onto the bollard

post or cleat on the disabled vessel without trapping the heaving line.

A standard ‘throw bag’ can be used as a messenger line. They are made

from polypropylene and can be thrown or used to float a line to the

disabled vessel.

A floating line (polypropylene), used

with a life ring, fender or lifejacket,

may be floated from upstream /

upwind, so that the current or wind

carries the line to the disabled vessel.

This can be slow and difficult to

achieve so is usually only attempted

in exceptional circumstances.

A rocket line thrower or shoulder

line-firing gun may be used to pass a

towline when conditions are such

that your vessel cannot get close

enough to the disabled craft to use a

heaving line. They are predominantly

used when forced to throw into

strong wind. Similar to a heaving line

aim high to allow the line to land

over the deck. Never aim directly at

the other vessel or its crew.

Preparing two

heaving lines is

recommended. If

the first pass is

unsuccessful then

the second line can

be tossed

immediately.

It is shock loading

that is the greatest

cause of towlines

parting or pulling

out fittings.


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5. Catenary Devices

A catenary is the curve or dip in a line caused either by the weight of the

line or by a weight attached to the line. If a towline is stretched taut

between two vessels any shock loading is transmitted directly through to

both vessels.

Having a catenary in the line means that part of any dynamic loading is

absorbed by having to first lift and stretch out the towline - the longer

the towline the more catenary

The space available on board many CRVs means that the length of

towline alone may not be enough to induce the desired catenary, so

additional weight may need to be added to the towline.

6. Drogues

A drogue slows a vessel down and produces greater directional

stability.

Drogues come in various designs and should be of a size

suitable for the vessel.

There are adjustable drogues that can be used for a range of

different sized vessels.

Deployed from the towed vessel’s stern a drogue will help to

prevent it surfing down the face of a wave or sheering from side

to side.

Drogues are useful when a towline has been shortened up in preparation

to enter harbour, when running a bar, or when towing in a following sea.

If a suitable patented drogue is not available, other equipment may be

used in its place but it needs to be robust enough to withstand the forces

involved. Warps streamed in a single line or in a bight, with objects

attached such as water containers and fenders (weighted down) have all

been used as drogues.

7. Kicker Hook

It is a device which can be used to fasten a towline to the ‘trailer eye’ (an

eyebolt on the waterline under the bow) of a trailer boat (a difficult and

potentially dangerous operation at sea).

“You must

familiarise yourself

with the operating

characteristics and

effectiveness of

drogues under

differing conditions.

The time to learn

about a drogue is

before you need to

deploy one.”

Section 10.4.8 from

SAR Seamanship

Reference Manual

(2001). Canadian

Coastguard.

It is shock loading

that is the greatest

cause of towlines

parting or pulling

out fittings.

“You must

familiarise yourself

with the operating

characteristics and

effectiveness of

drogues under

differing conditions.

The time to learn

about a drogue is

before you need to

deploy one.”

Section 10.4.8 from

SAR Seamanship

Reference Manual

(2001). Canadian

Coastguard.


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Many trailer boats do not have deck fittings of sufficient size or strength

to rely on for towing, with the exception of the trailer eye, and towing

from the trailer eye is the preferred method as it helps to lift the bow of

the towed vessel.

Any towline attached to the bow of a vessel will depress or pull down the

bow (referred to as a vessel trimmed by the head / bow). The smaller the

vessel the more pronounced this effect can be. Any vessel trimmed by

the head will be harder to control and will have a greater tendency to

yaw (swerve from side to side). When possible trailer boats should be

towed from the “trailer eye” to prevent this from occurring.

8. Towing Equipment Maintenance

All equipment used in towing should be checked regularly.

Any damaged or worn equipment should be replaced at the first

opportunity.

Any rope used should be from a reputable manufacturer or

supplier and have known ratings for strength and stretch.

Any hardware used such as shackles should be from a reputable

manufacturer or supplier and have known ratings for strength.

Any hardware used should be inspected regularly for signs of

corrosion or fractures.


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9 Forces in Towing

Most accidents that do occur during towing operations can

be traced back to insufficient preparation, inappropriate set

up, or inadequate monitoring of equipment and crew during

the tow. To appreciate the inherent dangers in towing an understanding

of the forces acting upon both the towed and towing vessels is essential.

9.1 Yawing Yawing is when the towed vessel swerves off course, and can endanger

both the towed vessel and CRV. To prevent or reduce a towed vessel

yawing:

make sure the tow line is pulling the towed vessel from a point

on its centreline.

decrease speed.

lengthen the towline.

ensure that both CRV and towed vessel are in step with each

other (on the same part of a different wave).

if possible trim the towed vessel down by the stern. Lower

outboards for example on smaller vessels, or move weight(s) to

the stern.

whenever possible tow trailer boats from the towing eye.

deploy a drogue or similar from the stern of the towed vessel.

engine on towed vessel centered and if necessary lash the tiller.

9.2 Burying the Bow The CRV can cause the towed vessel to bury its bow by getting the tow

out of step with the wave pattern, or by towing at too high a speed.

This is common in steep waves and can happen while travelling at any

angle into or before the sea. In a head sea burying the bow of the towed

vessel can create huge loadings on the tow line and risk swamping the

towed vessel. In a following sea there is the danger of the towed vessel

broaching. If possible always attach the towline to the towing eye of

Forces involved

include:

Static forces: those

forces that cause a

vessel to resist

motion. Bigger

vessels require

greater force to get

it moving.

Momentum: once

the vessel starts

moving it will

continue in same

direction. The

bigger it is or faster

it moves = harder

to stop or change

direction.

Friction resistance:

this is the water

drag on hull. The

faster speed =

more power to

keep it moving.

Form drag: this is

the effect of the

hull shape on the

ability to move the

vessel (changing

course and

maintaining

heading)

Activity:

Being Aware

Crew have a

responsibility to

maintain watch and

notify the Skipper if

they see anything of

concern.

Give the crew the

following list of issues

and ask them what

each may indicate and

what the response of

the crew / skipper

could be.

Anyone on board the

tow indicating

distress

Tow moving from

astern to one side

Towed vessel veering

back and forth

Towline stretching

and pulling

Towline unravelling

or fraying

Towline groaning or

overloaded

Towed vessel settling

in the water or

sinking

Securing points

moving or coming

loose

Bow of towed vessel

being swamped


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trailer boats to help lift the bow. Towing above the planing speeds

induces this problem much more readily than tows carried out at

displacement speeds.

9.3 Stopping and Swamping The towed vessel can cause the CRV to both stop and then to be

swamped by following seas if it has got out of step with the sea state

when being towed in a quartering or following sea. The towed vessel

falls behind one wave while the CRV is in front of the same, or another

wave. If the towed vessel buries its bow, its reserve buoyancy is enough

to dramatically slow down or stop its progress through the water. This in

turn affects the CRV which can be overrun by waves as its stern is held

down by the weight of the tow.

9.4 Being Overtaken by the Tow This occurs when the CRV and the towed vessel get out of step. The CRV

either slows down or stops, or the towed vessel accelerates down or

across a wave (with the possibility of broaching) and overtakes or

collides with the CRV. The same thing can happen if the CRV slows down

too quickly, and does not allow for a natural rate of deceleration for the

towed vessel. The heavier the vessel, and higher the initial speed, the

more momentum it will have.

All of the above hazards are likely to occur if the CRV and casualty are

out of step with one another, and they will all increase the risk of the

towline parting or pulling out fittings.

The general rule for

towing astern in

open water is to

use as long a tow

line as possible, and

always ensure the

vessels are in step

with each other.


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9.5 Towing Speed Displacement vessels should never be towed at or above their hull speed

because:

Fuel consumption rises considerably for the CRV.

Enormous strain is put on the towline and fittings as the towline

tries to literally drag the vessel up and through its own bow

wave.

The risk of pulling out a fitting or snapping the towline

increases.

Small vessels can be swamped and sunk while under tow purely

because they were towed at excessive speed.

Any loss of support to the towed vessel while planing, such as

wave effects, turning, change in weight distribution or change in

speed may well cause a rapid drop off the plane and a potential

hazard from the effects of rapid deceleration and / or yawing.

10. Towing Situations

10.1 Sinking Tow If time allows the vessel should be towed out of any shipping channels

and possibly beached. In shallow water and if safety permits pay out the

towline and buoy off its end so that it is visible on the surface. Note the

sunken vessels position and report the situation. Have a method of

cutting the tow line ready.

10.2 Vessel Aground For a vessel that has run aground on a falling tide, often by the time a

CRV arrives on scene, towing the vessel off is no longer possible. The

best that can be done is to secure its position and await the next flood

tide.

Approx Max towing

speed = Sq root of

waterline length in

feet x 1.34.

Safe towing speed

= 90% of approx

Max towing speed.

All towing

operations should

be carried out at

speeds suitable for

the conditions.

Any vessel that

sinks becomes the

responsibility of the

Local / Regional

Harbour Master or

MNZ depending on

its location. Units

must be aware of

their local

procedures &

protocols in regards

to sunken vessels.


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For a vessel aground on an incoming tide, all that may be needed is to

secure the vessel in position and wait for the tide to do the rest.

Before assisting a vessel aground, the CRV crew must make a thorough

analysis of the situation. Consider;

Are crew uninjured and accounted for?

Advise vessel’s crew to put on life jackets

Is the vessel damaged in any way, or taking on water?

Is the vessel leaking any fuel /oil?

What is the vessel’s draught?

No immediate attempt should be made to pull off a vessel that has been

or is suspected to have been seriously damaged or if there is any doubt

as to the vessel's ability to remain afloat.

If the CRV assessment reveals that the vessel will remain afloat, carefully

determine the refloating procedures to use. When preparing to tow free

a grounded vessel the Skipper and crew of the CRV must always assess

the possible hazards to their own vessel. There are too many cases of

one vessel attempting to help another, then subsequently running

aground or suffering damage to their own vessel in the process.

10.3 Heeling a Vessel Aground For any vessel with a deep keel, heeling it over to one side will effectively

reduce the draught. This is a method most commonly employed with

yachts. Lead a halyard from the mast to another vessel or a fixed object.

Care should be taken that the halyard used will not foul and put undue

strain on the yacht’s rig when it is heeled. The spreaders or crosstrees on

a yacht rig are designed to take compression loading from the standing

rigging. They are not designed to take large loads in a fore and aft

direction.

Before attempting

to tow off a

grounded vessel,

the skipper of the

CRV must answer

the question - is it

necessary?

Coastguard’s

primary role is

saving lives not

property.

Refloating the

casualty will

probably not be

considered a

success if you

dismast it in the

process!


11

10.4 Vessel at Anchor A disabled vessel will often have put down its anchor. If there is

sufficient sea room the anchor can be raised and the vessel allowed to

drift before setting up the towline. This at least allows a clear foredeck

prior to accepting the tow. If the vessel is close to a lee shore then the

towline may need to be attached prior to raising the anchor.

A problem can occur when a vessel is unable to raise its anchor. The

anchor may need to be ‘tripped ‘by the CRV. If the anchor cannot be

tripped, or the CRV Skipper decides that tripping the anchor is

unnecessarily hazardous, then it will need to be left behind. If the anchor

is left behind then a GPS position should be taken and the end of the

anchor rode buoyed so that it can be retrieved at a later date.

10.5 Towing Alongside or Barging There are 3 common ways in which a tow astern can be transferred to an

alongside tow:

• While Underway

• While at Anchor

• While on a Mooring

Towing alongside should only be attempted in calm to slight seas, and

for a short period of time. To give the greatest amount of control over

the tow the CRV should be tied alongside the vessel as far aft as possible

while still remaining secure alongside. With vessels smaller than the CRV

the positioning generally isn’t that critical, however with vessels the

same size or larger it becomes increasingly important.

• The CRV should be made fast using a bow line, stern line, and

spring lines to prevent the vessels surging.

• All lines should be positioned so that adjustments can be made

on board the CRV.

A bight of line or

preferably a short

length of chain is

passed around the

anchor rode and

pulled slowly and

gently along the

rode until it comes

in contact with the

anchor. The anchor

is then pulled out

by the CRV.

Securing the CRV

so that its bow is

pointed in slightly

ensures that when

moving ahead the

water pressure

created is keeping

the vessels

together, not trying

to force them

apart.


12

• Once secured alongside all slack in the lines should be taken up,

with the bow of the CRV pointing in towards the other vessel by

about 10-15°.

• There are no hard and fast rules as to exactly how the tow is

made fast, each vessel will be different as the position of the

cleats or posts available will determine how the tow is finally

secured.

10.6 Berthing a Tow Before committing to any close quarter manoeuvres it is imperative to

test manoeuvrability. Performing a figure of eight then coming to a stop

will give you an indication of your turning circle and stopping distance.

Sometimes even a ‘safe berth’ can present difficulties if there is a strong

wind or tide. CRVs usually have more than adequate power

and manoeuvrability to berth in adverse conditions, but that

may not be the case with another vessel tied alongside.

11. Summary of Standard Towing Practice

Standard practice that should be adopted when towing;

• Operate with an extended tow line in open water, generally the

longer the better.

• Always try to keep the towed vessel and CRV ‘in step’.

• As necessary deploy a drogue from the towed vessel to reduce

its potential to yaw.

• Trim the towed vessel down by the stern if possible.

• As necessary employ a catenary device in the tow line to

minimise snatch loading.

• Tow at a safe speed – For a displacement vessel with

consideration for its max hull speed, and for all vessels at all

times a speed suitable for the conditions.

When planning to

berth a tow it

should always be

remembered that

the CRV is obliged

to secure the towed

vessel to a safe

berth not

necessarily its

customary berth.

Activity:

Towing SAP.

The SAP process is vital

in preparing for a tow

(see CRM Module).

Gathering information

to assist in the planning

phase is vital (assessing)

– but what information

should be collected?

Visual assessment

• Have the crew work

in small groups. Give

each group one

aspect of visual

assessment (from

vessel state, people

on board and

environmental

factors) and have

them write a list of

dangers and other

factors that should be

considered as they

plan for the tow.

Towing Techniques - Wikispaces · Towing Techniques – Version 1 (2013) ... 10.4 Vessel at Anchor...

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